CNC Plasma Cutter Filter Gets The Slag Out

No matter what kind of tools and materials you use in your shop, chances are pretty good that some process is going to release something that you don’t want to breathe. Table saw? Better deal with that wood dust. 3D-printer? We’ve discussed fume control ad nauseam. Soldering? It’s best not to inhale those flux fumes. But perhaps nowhere is fume extraction more important than in the metal shop, where vaporized bits of metal can wreak respiratory havoc.

Reducing such risks was [Shane Wighton]’s rationale behind this no-clean plasma cutter filter. Rather than a water table to collect cutting dross, his CNC plasma cutter is fitted with a downdraft table to suck it away. The vivid display of sparks shooting out of the downdraft fans belied its ineffectiveness, though. [Shane]’s idea is based on the cyclonic principle common to woodshop dust collectors and stupidly expensive vacuum cleaners alike. Plastic pipe sections, split in half lengthwise and covered in aluminum tape to make them less likely to catch on fire from the hot sparks, are set vertically in the air path. The pipes are arranged in a series of nested “S” shapes, offering a tortuous path to the spark-laden air as it exits the downdraft.

The video below shows that most of the entrained solids slow down and drop to the bottom of the filter; some still pass through, but testing with adhesive sheets shows the metal particles in the exhaust are much reduced. We like the design, especially the fact that there’s nothing to clog or greatly restrict the airflow.

Looking for more on CNC plasma cutter builds? We’ve got you covered, from just the basics to next-level.

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Hacked Protective Gear Keeps Doctor Safe In The Hot Zone

It’s rarely a wise idea to put a plastic bag over one’s head, but when the choice is between that and possibly being exposed to a dangerous virus, you do what you have to. So you might as well do it right and build a field-expedient positive pressure hood.

We’ve all been keeping tabs on the continuing coronavirus outbreak in China, but nobody is following as closely as our many friends in China. Hackaday contributor [Naomi Wu] is in from Shenzhen, posting regularly from the quarantined zone, and she found this little gem of ingenuity from a [Doctor Cui] in one of the hospitals in Wuhan. Quarantines and travel restrictions have put personal protective equipment like masks and gowns in limited supply, with the more advanced gear needed by those deal most closely with coronavirus patients difficult to come by.

There’s no build information, but from the pictures we can guess at what [Dr. Cui] came up with. The boxy bit is an AirPro Car, a HEPA filter meant to clean the cabin air in a motor vehicle. He glued on a USB battery pack to power it, used a scrap of plastic and some silicone adhesive to adapt a heat-moisture exchange filter from a mechanical ventilator to the AirPro’s outlet, and stuck the tube into a plastic bag sealed around his neck. The filter provides dry, positive pressure air to keep the bag from fogging up, and to keep [Dr. Cui] from asphyxiating. Plus he’s protected from droplet contact, which is a big plus over simple paper masks.

With the news always so dark, it’s heartening to see stories of ingenuity like this. We wish [Dr. Cui] and all our friends in China the best during this outbreak.

Solving The Mysteries Of Grounding While Improving A Power Supply

Grounding problems and unwanted noise in electrical systems can often lead to insanity. It can seem like there’s no method to the madness when an electrical “gremlin” caused by one of these things pops its head out. When looking more closely, however, these issues have a way of becoming more obvious. In a recent video, [Fesz Electronics] shows us how to investigate some of these problems by looking at a small desktop power supply, modelling it in LTSpice, and reducing the noise on the power supply’s output.

While everything in this setup is properly grounded, including the power supply and oscilloscope, the way the grounding systems interact can contribute to the high amount of noise. This was discovered by isolating the power supply from earth ground using electrical tape (not recommended as a long-term solution) and seeing that the noise was reduced. However, the ripple increased substantially, so a more permanent fix was needed. For that, the power supply was modelled in LTSpice. This is where a key discovery was made: since all the parts of the power supply aren’t ideal, noise can be introduced from the actual real-life electrical behavior of some of the parts. In this case, it was non-ideal capacitance in the transformer.

According to the model, this power supply could be improved by adding a larger capacitor across the output leads, and also by increasing their inductance. A large capacitor was soldered in the power supply and an iron ferrule was added, which decreased the noise level from 100 mV to around 20. Still not perfect, but a much needed improvement to the simple power supply. If, on the other hand, you want to make sure you eliminate that transformer’s capacitance completely, you can always go with a transformerless power supply. That carries other risks, though.

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Fail Of The Week: Ambitious Vector Network Analyzer Fails To Deliver

If you’re going to fail, you might as well fail ambitiously. A complex project with a lot of subsystems has a greater chance of at least partial success, as well as providing valuable lessons in what not to do next time. At least that’s the lemonade [Josh Johnson] made from his lemon of a low-cost vector network analyzer.

For the uninitiated, a VNA is a versatile test instrument for RF work that allows you to measure both the amplitude and the phase of a signal, and it can be used for everything from antenna and filter design to characterizing transmission lines. [Josh] decided to port a lot of functionality for his low-cost VNA to a host computer and concentrate on the various RF stages of the design. Unfortunately, [Josh] found the performance of the completed VNA to be wanting, especially in the phase measurement department. He has a complete analysis of the failure modes in his thesis, but the short story is poor filtering of harmonics from the local oscillator, unexpected behavior by the AD8302 chip at the heart of his design, and calibration issues. Confounding these issues was the time constraint; [Josh] might well have gotten the issues sorted out had the clock not run out on the school year.

After reading through [Josh]’s description of his project, which was a final-year project and part of his thesis, we feel like his rating of the build as a failure is a bit harsh. Ambitious, perhaps, but with a spate of low-cost VNAs coming on the market, we can see where he got the inspiration. We understand [Josh]’s disappointment, but there were a lot of wins here, from the excellent build quality to the top-notch documentation.

Sensor Filters For Coders

Anybody interested in building their own robot, sending spacecraft to the moon, or launching inter-continental ballistic missiles should have at least some basic filter options in their toolkit, otherwise the robot will likely wobble about erratically and the missile will miss it’s target.

What is a filter anyway? In practical terms, the filter should smooth out erratic sensor data with as little time lag, or ‘error lag’ as possible. In the case of the missile, it could travel nice and smoothly through the air, but miss it’s target because the positional data is getting processed ‘too late’. The simplest filter, that many of us will have already used, is to pause our code, take about 10 quick readings from our sensor and then calculate the mean by dividing by 10. Incredibly simple and effective as long as our machine or process is not time sensitive – perfect for a weather station temperature sensor, although wind direction is slightly more complicated. A wind vane is actually an example of a good sensor giving ‘noisy’ readings: not that the sensor itself is noisy, but that wind is inherently gusty and is constantly changing direction.

It’s a really good idea to try and model our data on some kind of computer running software that will print out graphs – I chose the Raspberry Pi and installed Jupyter Notebook running Python 3.

The photo on the left shows my test rig. There’s a PT100 probe with it’s MAX31865 break-out board, a Dallas DS18B20 and a DHT22. The shield on the Pi is a GPS shield which is currently not used. If you don’t want the hassle of setting up these probes there’s a Jupyter Notebook file that can also use the internal temp sensor in the Raspberry Pi. It’s incredibly quick and easy to get up and running.

It’s quite interesting to see the performance of the different sensors, but I quickly ended up completely mangling the data from the DS18B20 by artificially adding randomly generated noise and some very nasty data spikes to really punish the filters as much as possible. Getting the temperature data to change rapidly was effected by putting a small piece of frozen Bockwurst on top of the DS18B20 and then removing it again.

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I Love The Smell Of ABS Plastic In The Morning

One lesson we can learn from the Vietnam War documentary Apocalypse Now is that only crazy people like terrible smells just for fun. Surely Lt. Col. Kilgore would appreciate the smell of 3D printers as well, but for those among us who are a little less insane, we might want a way to eliminate the weird (and not particularly healthy) smell of melting ABS plastic.

While a simple solution would be a large fume hood or a filter to prevent inhaling the fumes, there are more elegant solutions to this problem. [Mark]’s latest project uses an electrostatic precipitator (ESP) to remove the volatile plastic particles from the air. Essentially it is a wire with a strong voltage applied to it enclosed in a vessel of some sort. The voltage charges particles, which then travel to a collecting electrode. Commercial offerings also include an X-ray generator to help clean the air, but [Mark] found this to be prohibitively expensive.

The ESP is built into a small tube through with the air can flow, and the entire device itself is housed in the printing enclosure. The pictures show the corona discharge in the device, and [Mark] plans to test it over the next few months to determine its effectiveness. He does note, however, that the electrostatic discharge creates ozone, which has its own set of problems, so he recommends against building one on your own. Ozone at least still smells like victory.

Fluorescence Microscope On A Hacker’s Budget

Some of biology’s most visually striking images come from fluorescence microscopes. Their brilliant colors on black look like a neon sign from an empty highway. A brand new fluorescence microscope is beyond a hacker’s budget and even beyond some labs’, but there are ways to upgrade an entry-level scope for the cost of a few cups of coffee. [Justin Atkin] of The Thought Emporium published a scope hacking video which can also be seen below. He is becoming a reputed scope modder.

This video assumes a couple of things for the $10 price tag. The first premise is that you already have a scope, a camera adapter, and a camera capable of shooting long exposures. The second premise is that you are willing to break the seals and open the scope to make some reversible mods. Since you are reading Hackaday, maybe that is a given.

The premise is simple compared to the build, which is not rocket surgery, the light source from below illuminates the subject like a raver, and the filter removes any light that isn’t spectacular before it gets to the camera.

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